This invention relates to certain monocyclopentadienyl metal compounds of a Group IV B transition metal of the Periodic Table of Elements, to a catalyst system comprising a monbcyclopentadienyl Group IV B transition metal compound and an alumoxane, and to a process using such catalyst system for the production of polyolefins, particularly polyethylene, polypropylene and xcex1-olefin copolymers of ethylene and propylene having a high molecular weight. The catalyst system is highly active at low ratios of aluminum to the Group IV B transition metal, hence catalyzes the production of a polyolefin product containing low levels of catalyst metal residue. Titanium species of the catalyst are stable at high pressures in unsupported form, unlike their bis-cyclopentadienyl titanium compound counterparts, and exhibit the ability to catalyze the incorporation of higher xcex1-olein comonomer contents for production of higher molecular weight xcex1-olefin copolymers than analogous zirconium and hafnium species of a monocyclopentadienyl transition metal compound.
As is well known, various processes and catalysts exist for the homopolymerization or copolymerization of olefins. For many applications it is of primary importance for a polyolefin to have a high weight average molecular weight while having a relatively narrow molecular weight distribution. A high weight average molecular weight, when accompanied by a narrow molecular weight distribution, provides a polyolefin or an ethylene-xcex1-olefin copolymer with high strength properties.
Traditional Ziegler-Natta catalysts systemxe2x80x94a transition metal compound cocatalyzed by an aluminum alkylxe2x80x94are capable of producing polyolefins having a high molecular weight but a broad molecular weight distribution.
More recently a catalyst system has been developed wherein the transition metal compound has two or more cyclopentadienyl ring ligandsxe2x80x94such transition metal compound being referred to as a metallocenexe2x80x94which catalyzes the production of olefin monomers to polyolefins. Accordingly, metallocene compounds of a Group IV B metal, particularly, titanocenes and zirconocenes, have been utilized as the transition metal component in such xe2x80x9cmetallocenexe2x80x9d containing catalyst system for the production of polyolefins and ethylene-xcex1-olefin copolymers. When such metallocenes are cocatalyzed with an aluminum alkylxe2x80x94as is the case with a traditional type Ziegler-Natta catalyst systemxe2x80x94the catalytic activity of such metallocene catalyst system is generally too low to be of any commercial interest.
It has since become known that such metallocenes may be cocatalyzed with an alumoxanexe2x80x94rather than an aluminum alkylxe2x80x94to provide a metallocene catalyst system of high activity for the production of polyolefins.
The zirconium metallocene species, as cocatalyzed or activated with an alumoxane, are commonly more active than their hafnium or titanium analogous for the polymerization of ethylene alone or together with an xcex1-olefin comonomer. When employed in a non-supported formxe2x80x94i.e., as a homogeneous or soluble catalyst systemxe2x80x94to obtain a satisfactory rate of productivity even with the most active zirconium species of metallocene typically requires the use of a quantity of alumoxane activator sufficient to provide an aluminum atom to transition metal atom ratio (Al:TM) of at least greater than 1000:1; often greater than 5000:1, and frequently on the order of 10,000:1. Such quantities of alumoxane impart to a polymer produced with such catalyst system an undesirable content of catalyst metal residue, i.e., an undesirable xe2x80x9cashxe2x80x9d content (the nonvolatile metal content). In high pressure polymerization procedures using soluble catalyst systems wherein the reactor pressure exceeds about 500 bar only the zirconium or hafnium species of metallocenes may be used. Titanium species of metallocenes are generally unstable at such high pressures unless deposited upon a catalyst support.
A wide variety of Group IV B transition metal compounds have been named as possible candidates for an alumoxane cocatalyzed catalyst system. Although bis(cyclopentadienyl) Group IV B transition metal compounds have been the most preferred and heavily investigated for use in alumoxane activated catalyst systems for polyolefin production, suggestions have appeared that mono and tris(cyclopentadienyl) transition metal compounds may also be useful. See, for example U.S. Pat. Nos. 4,522,982; 4,530,914 and 4,701,431. Such mono(cyclopentadienyl) transition metal compounds as have heretofore been suggested as candidates for an alumoxane activated catalyst system are mono(cyclopentadienyl) transition metal trihalides and trialkyls.
More recently, International Publication No. WO 87/03887 describes the use of a composition comprising a transition metal coordinated to at least one cyclopentadienyl and at least one heteroatom ligand as a transition metal component for use in an alumoxane activated catalyst system for xcex1-olefin polymerization. The composition is broadly defined as a transition metal, preferably of Group IV B of the Periodic Table, which is coordinated with at least one cyclopentadienyl ligand and one to three heteroatom ligands, the balance of the transition metal coordination requirement being satisfied with cyclopentadienyl or hydrocarbyl ligands. Catalyst systems described by this reference are illustrated solely with reference to transition metal compounds which are metallocenes, i.e., bis(cyclopentadienyl) Group IV B transition metal compounds.
Even more recently, at the Third Chemical Congress of North American held in Toronto, Canada in June 1988, John Bercaw reported upon efforts to use a compound of a Group III B transition metal coordinated to a single cyclopentadienyl heteroatom bridged ligand as a catalyst system for the polymerization of olefins. Although some catalytic activity was observed under the conditions employed, the degree of activity and the properties observed in the resulting polymer product were discouraging of a belief that such monocyclopentadienyl transition metal compound could be usefully employed for commercial polymerization processes.
A need still exists for discovering catalyst systems that permit the production of higher molecular weight polyolefins and desirably with a narrow molecular weight distribution. It is further desirable that a catalyst be discovered which, within reasonable ranges of ethylene to xcex1-olefin monomer ratios, will catalyze the incorporation of higher contents of xcex1-olefin comonomers in the production of ethylene-xcex1-olefins copolymers.
The catalyst system of this invention comprises a transition metal component from Group IV B of the Periodic Table of the Elements (CRC Handbook of Chemistry and Physics, 68th ed. 1987-1988) and an alumoxane component which may be employed in solution, slurry or bulk phase polymerization procedure to produce a polyolefin of high weight average molecular weight and relatively narrow molecular weight distribution.
The xe2x80x9cGroup IV B transition metal componentxe2x80x9d of the catalyst system is represented by the formula: 
wherein: M is Zr, Hf or Ti in its highest formal oxidation state (+4, d0 complex);
(C2H5xe2x88x92yxe2x88x92xRx) is a cyclopentadienyl ring which is substituted with from zero to five substituent groups R, xe2x80x9cxxe2x80x9d is 0, 1, 2, 3, 4 or 5 denoting the degree of substitution, and each substituent group R is, independently, a radical selected from a group consisting of C1-C20 hydrocarbyl radicals, substituted C1-C20 hydrocarbyl radicals wherein one or more hydrogen atoms is replaced by a halogen radical, an amido radical, a phosphido radical, and alkoxy radical or any other radical containing a Lewis acidic or basic functionality; C1-C20 hydrocarbyl-substituted metalloid radicals wherein the metalloid is selected from the Group IV A of the Periodic Table of Elements; halogen radical, amido radicals, phosphido radicals, alkoxy radicals, alkylborido radicals or any other radical containing Lewis acidic or basic functionality; or (C2H5xe2x88x92yxe2x88x92xRx) is a cyclopentadienyl ring in which at least two adjacent R-groups are joined forming a C4-C20 ring to give a saturated or unsaturated polycyclic cyclopentadienyl ligand such as indenyl, tetrahydroindenyl, fluorenyl or octahydrofluorenyl;
(JRxe2x80x2zxe2x88x921xe2x88x92y) is a heteroatom ligand in which J is an element with a coordination number of three from Group V A or an element with a coordination number of two from Group VI A of the Periodic Table of Elements, preferably nitrogen, phosphorus, oxygen or sulfur, and each Rxe2x80x2 is, independently a radical selected from a group consisting of C1-C20 hydrocarbyl radicals, substituted C1-C20 hydrocarbyl radicals wherein one or more hydrogen atoms are replaced by a halogen radical, an amido radical, a phosphido radical, an alkoxy radical or any other radical containing a Lewis acidic or basic functionality, and xe2x80x9czxe2x80x9d is the coordination number of the element J;
each Q may be independently any univalent anionic ligand such as a halide, hydride, or substituted or unsubstituted C1-C20 hydrocarbyl, alkoxide, aryloxide, amide, arylamide, phosphide or arylphosphide, provided that where any Q is a hydrocarbyl such Q is different from (C2H5xe2x88x92yxe2x88x92xRx), or both Q together may be an alkylidene or a cyclometallated hydrocarbyl or any other divalent anionic chelating ligand;
xe2x80x9cyxe2x80x9d is 0 or 1 when w is greater than 0; y is 1 when w is 0; when xe2x80x9cyxe2x80x9d is 1, T is a covalent bridging group containing a Group IV A or V A element such as, but not limited to, a dialkyl, alkylaryl or diaryl silicon or germanium radical, alkyl or aryl phosphine or amine radical, or a hydrocarbyl radical such as methylene, ethylene and the like;
L is a neutral Lewis base such as diethylether, tetraethylammonium chloride, tetrahydrofuran, dimethylaniline, aniline, trimethylphosphine, n-butylamine, and the like; and xe2x80x9cwxe2x80x9d is a number from 0 to 3. L can also be a second transition metal compound of the same type such that the two metal centers M and Mxe2x80x2 are bridged by Q and Qxe2x80x2, wherein Mxe2x80x2 has the same meaning as M and Qxe2x80x2 has the same meaning as Q. Such dimeric compounds are represented by the formula: 
The alumoxane component of the catalyst may be represented by the formulas: (R3xe2x80x94Alxe2x80x94O)m; R4(R5xe2x80x94Alxe2x80x94O)mxe2x80x94AlR6 or mixtures thereof, wherein R3-R6 are, independently, a C1-C5 alkyl group or halide and xe2x80x9cmxe2x80x9d is an integer ranging from 1 to about 50 and preferably is from about 13 to about 25.
Catalyst systems of the invention may be prepared by placing the xe2x80x9cGroup IV B transition metal componentxe2x80x9d and the alumoxane component in common solution in a normally liquid alkane or aromatic solvent, which solvent is preferably suitable for use as a polymerization diluent for the liquid phase polymerization of an olefin monomer.
Those species of the Group IV B transition metal component wherein the metal is titanium have been found to impart beneficial properties to a catalyst system which are unexpected in view of what is known about the properties of bis(cyclopentadienyl) titanium compounds which are cocatalyzed by alumoxanes. Whereas titanocenes in their soluble form are generally unstable in the presence of aluminum alkyls, the monocyclopentadienyl titanium metal components of this invention, particularly those wherein the heteroatom is nitrogen, generally exhibit greater stability in the presence of aluminum alkyls, higher catalyst activity rates and higher xcex1-olefin comonomer incorporation.
Further, the titanium species of the Group IV B transition metal component catalyst of this invention generally exhibit higher catalyst activities and the production of polymers of greater molecular weight and xcex1-olefin comonomer contents than catalyst systems prepared with the zirconium or hafnium species of the Group IV B transition metal component.
A typical polymerization process of the invention such as for the polymerization or copolymerization of ethylene comprises the steps of contacting ethylene or C3-C20 xcex1-olefins alone, or with other unsaturated monomers including C3-C20 xcex1-olefins, C5-C20 diolefins, and/or acetylenically unsaturated monomers either alone or in combination with other olefins and/or other unsaturated monomers, with a catalyst comprising, in a suitable polymerization diluent, the Group IV B transition metal component illustrated above; and a methylalumoxane in an amount to provide a molar aluminum to transition metal ratio of from about 1:1 to about 20,000:1 or more; and reacting such monomer in the presence of such catalyst system at a temperature of from about xe2x88x92100xc2x0 C. to about 300xc2x0 C. for a time of from about 1 second to about 10 hours to produce a polyolefin having a weight average molecular weight of from about 1,000 or less to about 5,000,000 or more and a molecular weight distribution of from about 1.5 to about 15.0.
The Group IV B transition metal component of the catalyst system is represented by the general formula: 
wherein M is Zr, Hf or Ti in its highest formal oxidation state (+4, d0 complex);
(C2H5xe2x88x92yxe2x88x92xRx) is a cyclopentadienyl ring which is substituted with from zero to five substituent groups R, xe2x80x9cxxe2x80x9d is 0, 1, 2, 3, 4 or 5 denoting the degree of substitution, and each substituent group R is, independently, a radical selected from a group consisting of C1-C20 hydrocarbyl radicals, substituted C1-C20 hydrocarbyl radicals wherein one or more hydrogen atoms is replaced by a halogen radical, an amido radical, a phosphido radical, an alkoxy radical or any other radical containing a Lewis acidic or basic functionality, C1-C20 hydrocarbyl-substituted metalloid radicals wherein the metalloid is selected from the Group IV A of the Periodic Table of Elements; and halogen radicals, amido radicals, phosphido radicals, alkoxy radicals, alkylborido radicals or any other radical containing Lewis acidic or basic functionality; or (C2H5xe2x88x92yxe2x88x92xRx) is a cyclopentadienyl ring in which two adjacent R-groups are joined forming C4-C20 ring to give a saturated or unsaturated polycyclic cyclopentadienyl ligand such as indenyl, tetrahydroindenyl, fluorenyl or octahydrofluorenyl;
(JRxe2x80x2zxe2x88x921xe2x88x92y) is a heteroatom ligand in which J is an element with a coordination number of three from Group V A or an element with a coordination number of two from Group VI A of the Periodic Table of Elements, preferably nitrogen, phosphorus, oxygen or sulfur with nitrogen being preferred, and each Rxe2x80x2 is, independently a radical selected from a group consisting of C1-C20 hydrocarbyl radicals, substituted C1-C20 hydrocarbyl radicals wherein one or more hydrogen atoms is replaced by a halogen radical, an amido radical, a phosphido radical, and alkoxy radical or any other radical containing a Lewis acidic or basic functionality, and xe2x80x9czxe2x80x9d is the coordination number of the element J;
each Q is, independently, any univalent anionic ligand such as a halide, hydride, or substituted or unsubstituted C1-C20 hydrocarbyl, alkoxide, aryloxide, amide, arylamide, phosphide or arylphosphide, provided that where any Q is a hydrocarbyl such Q is different from (C2H5xe2x88x92yxe2x88x92xRx), or both Q together may be an alkylidene or a cyclometallated hydrocarbyl or any other divalent anionic chelating ligand;
xe2x80x9cyxe2x80x9d is 0 or 1 when w is greater than 0, and y is 1 when w equals 0; when xe2x80x9cyxe2x80x9d is 1, T is a covalent bridging group containing a Group IV A or V A element such as, but not limited to, a dialkyl, alkylaryl or diaryl silicon or germanium radical, alkyl or aryl phosphine or amine radical, or a hydrocarbyl radical such as methylene, ethylene and the like; and
L is a neutral Lewis base such as diethylether, tetrahydrofuran, dimethylaniline, aniline, trimethylphosphine, n-butylamine, and the like; and xe2x80x9cwxe2x80x9d is a number from 0 to 3; L can also be a second transition metal compound of the same type such that the two metal centers M and Mxe2x80x2 are bridged by Q and Qxe2x80x2, wherein Mxe2x80x2 has the same meaning as M and Qxe2x80x2 has the same meaning as Q. Such compounds are represented by the formula: 
Examples of the T group which are suitable as a constituent group of the Group IV B transition metal component of the catalyst system are identified in column 1 of Table 1 under the heading xe2x80x9cTxe2x80x9d.
Exemplary hydrocarbyl radicals for Q are methyl, ethyl, propyl, butyl, amyl, isoamyl, hexyl, isobutyl, heptyl, octyl, nonyl, decyl, cetyl, 2-ethylhexyl, phenyl and the like, with methyl being preferred. Exemplary halogen atoms for Q include chlorine, bromine, fluorine and iodine, with chlorine being preferred. Exemplary alkoxides and aryloxides for Q are methoxide, phenoxide and substituted phenoxides such as 4-methylphenoxide. Exemplary amides of Q are dimethylamide, diethylamide, methylethylamide, di-t-butylamide, diisoproylamide and the like. Exemplary aryl amides are diphenylamide and any other substituted phenyl amides. Exemplary phosphides of Q are diphenylphosphide, dicyclohexylphosphide, diethylphosphide, dimethylphosphide and the like. Exemplary alkyldiene radicals for both Q together are methylidene, ethylidene and propylidene. Examples of the Q group which are suitable as a constituent group or element of the Group IV B transition metal component of the catalyst system are identified in column 4 of Table 1 under the heading xe2x80x9cQxe2x80x9d.
Suitable hydrocarbyl and substituted hydrocarbyl radicals, which may be substituted as an R group for at least one hydrogen atom in the cyclopentadienyl ring, will contain from 1 to about 20 carbon atoms and include straight and branched alkyl radicals, cyclic hydrocarbon radicals, alkyl-substituted cyclic hydrocarbon radicals, aromatic radicals and alkyl-substituted aromatic radicals, amido-substituted hydrocarbon radicals, phosphido-substituted hydrocarbon radicals, alkoxy-substituted hydrocarbon radicals, and cyclopentadienyl rings containing one or more fused saturated or unsaturated rings. Suitable organometallic radicals, which may be substituted as an R group for at least one hydrogen atom in the cyclopentadienyl ring, include trimethylsilyl, triethylsilyl, ethyldimethylsilyl methyldiethylsilyl, triphenylgermyl, trimethylgermyl and the like. Other suitable radicals that may be substituted for one or more hydrogen atom in the cyclopentadienyl ring include halogen radicals, amido radicals, phosphido radicals, alkoxy radicals, alkyl boride radicals and the like. Examples of cyclopentadienyl ring groups (C2H5xe2x88x92yxe2x88x92xRx) which are suitable as a constituent group of the Group IV B transition metal component of the catalyst system are identified in Column 2 of Table 1 under the heading (C2H5xe2x88x92yxe2x88x92xRx).
Suitable hydrocarbyl and substituted hydrocarbyl radicals, which may be substituted as an Rxe2x80x2 group for at least one hydrogen atom in the heteroatom J ligand group, will contain from 1 to about 20 carbon atoms and include straight and branched alkyl radicals, cyclic hydrocarbon radicals, alkyl-substituted cyclic hydrocarbon radicals, aromatic radicals, alkyl-substituted aromatic radicals, halogen radicals, amido radicals, phosphido radicals and the like. Examples of heteroatom ligand groups (JRxe2x80x2zxe2x88x921xe2x88x92y) which are suitable as a constituent group of the Group IV B transition metal component of the catalyst system are identified in column 3 of Table 1 under the heading (JRxe2x80x2zxe2x88x921xe2x88x92y).
Table 1 depicts representative constituent moieties for the xe2x80x9cGroup IV B transition metal componentxe2x80x9d, the list is for illustrative purposes only and should not be construed to be limiting in any way. A number of final components may be formed by permuting all possible combinations of the constituent moieties with each other. Illustrative compounds are: dimethylsilyltetramethylcyclopentadienyl-tert-butylamido zirconium dichloride, dimethylsilyltetramethylcyclopentadienyl-tert-butylamido hafnium dichloride, dimethylsilyl-tert-butylcyclopentadienyl-tert-butylamido zirconium dichloride, dimethylsilyl-tert-butylcyclopentadienyl-tert-butylamido hafnium dichloride, dimethylsilyltrimethylsilylcyclopentadienyl-tert-butylamido zirconium dichloride, dimethylsilyltetramethylcyclopentadienylphenylamido zirconium dichloride, dimethylsilyltetramethylcyclopentadienylphenylamido hafnium dichloride, methylphenylsilyltetramethylcyclopentadienyl-tert-butylamido zirconium dichloride, methylphenylsilyltetramethylcyclopentadienyl-tert-butylamido hafnium dichloride, methylphenylsilyltetramethylcyclopentadienyl-t-butylamido hafnium dimethyl, dimethylsilyltetramethylcyclopentadienyl-p-n-butylphenylamido zirconium dichloride, dimethylsilyltetramethylcyclopentadienyl-p-n-butylphenylamido hafnium dichloride.
As noted, titanium species of the Group IV B transition metal compound have generally been found to yield catalyst systems which in comparison to their zirconium or hafnium analogus, are of higher activity and xcex1-olefin comonomer incorporating ability. Illustrative, but not limiting of the titanium species which exhibit such superior properties are methylphenylsilyltetramethylcyclopentadienyl-tert-butylamido titanium dichloride, dimethylsilyltetramethylcyclopentadienyl-p-n-butylphenylamido titanium dichloride, dimethylsilyltetramethylcyclopentadienyl-p-methoxyphenylamido titanium dichloride, dimethylsilyl-tert-butylcyclopentadienyl-2,5-di-tert-butylphenylamido titanium dichloride, dimethylsilylindenyl-tert-butylamido titanium dichloride, dimethylsilyltetramethylcyclopentadienylcyclohexylamido titanium dichloride, dimethylsilylfluorenylcyclohexylamido titanium dichloride, dimethylsilyltetramethylcyclopentadienylphenylamido titanium dichloride, dimethylsilyltetramethylcyclopentadienyl-tert-butylamido titanium dichloride, dimethylsilyltetramethylcyclopentadienylcyclododecylamido titanium dichloride, and the like.
For illustrative purposes, the above compounds and those permuted from Table 1 do not include the neutral Lewis base ligand (L). The conditions under which complexes containing neutral Lewis base ligands such as ether or those which form dimeric compounds is determined by the steric bulk of the ligands about the metal center. For example, the t-butyl group in Me2Si(Me4C5)(N-t-Bu)ZrCl2 has greater steric requirements than the phenyl group in Me2Si(Me4C5)(NPh)ZrCl2.Et2O thereby not permitting ether coordination in the former compound. Similarly, due to the decreased steric bulk of the trimethylsilylcyclopentadienyl group in [Me2Si(Me3SiC5H3)(N-t-Bu)ZrCl2]2 versus that of the tetramethylcyclopentadienyl group in Me2Si(Me4C5)(N-t-Bu)ZrCl2, the former compound is dimeric and the latter is not.
Generally the bridged species of the Group IV B transition metal compound (xe2x80x9cyxe2x80x9d=1) are preferred. These compounds can be prepared by reacting a cyclopentadienyl lithium compound with a dihalo compound whereupon a lithium halide salt is liberated and a monohalo substituent becomes covalently bound to the cyclopentadienyl compound. The so substituted cyclopentadienyl reaction product is next reacted with a lithium salt of a phosphide, oxide, sulfide or amide (for the sake of illustrative purposes, a lithium amide) whereupon the halo element of the monohalo substituent group of the reaction product reacts to liberate a lithium halide salt and the amine moiety of the lithium amide salt becomes covalently bound to the substituent of the cyclopentadienyl reaction product. The resulting amine derivative of the cyclopentadienyl product is then reacted with an alkyl lithium reagent whereupon the labile hydrogen atoms, at the carbon atom of the cyclopentadienyl compound and at the nitrogen atom of the amine moiety covalently bound to the substituent group, react with the alkyl of the lithium alkyl reagent to liberate the alkane and produce a dilithium salt of the cyclopentadienyl compound. Thereafter the bridged species of the Group IV B transition metal compound is produced by reacting the dilithium salt cyclopentadienyl compound with a Group IV B transition metal preferably a Group IV B transition metal halide.
Unbridged species of the Group IV B transition metal compound can be prepared from the reaction of a cyclopentadienyl lithium compound and a lithium salt of an amine with a Group IV B transition metal halide.
Suitable, but not limiting, Group IV B transition metal compounds which may be utilized in the catalyst system of this invention include those bridged species (xe2x80x9cyxe2x80x9d=1) wherein the T group bridge is a dialkyl, diaryl or alkylaryl silane, or methylene or ethylene. Exemplary of the more preferred species of bridged Group IV B transition metal compounds are dimethylsilyl, methylphenylsilyl, diethylsilyl, ethylphenylsilyl, diphenylsilyl, ethylene or methylene bridged compounds. Most preferred of the bridged species are dimethylsilyl, diethylsilyl and methylphenylsilyl bridged compounds.
Suitable Group IV B transition metal compounds which are illustrative of the unbridged (xe2x80x9cyxe2x80x9d=0) species which may be utilized in the catalyst systems of this invention are exemplified by pentamethylcyclopentadienyldi-t-butylphosphinodimethyl hafnium; pentamethylcyclopentadienyldi-t-butylphosphinomethylethyl hafnium; cyclopentadienyl-2-methylbutoxide dimethyl titanium.
To illustrate members of the Group IV B transition metal component, select any combination of the species in Table 1. An example of a bridged species would be dimethylsilyclopentadienyl-t-butylamidodichloro zirconium; an example of an unbridged species would be cyclopentadienyldi-t-butylamidodichloro zirconium.
Generally, wherein it is desired to produce an xcex1-olefin copolymer which incorporates a high content of xcex1-olefin, the species of Group IV B transition metal compound preferred is one of titanium. The most preferred species of titanium metal compounds are represented by the formula: 
wherein Q, L, Rxe2x80x2, R, xe2x80x9cxxe2x80x9d and xe2x80x9cwxe2x80x9d are as previously defined and R1 and R2 are each independently a C1 to C20 hydrocarbyl radicals, substituted C1 to C20 hydrocarbyl radicals wherein one or more hydrogen atom is replaced by a halogen atom; R1 and R2 may also be joined forming a C3 to C20 ring which incorporates the silicon bridge.
The alumoxane component of the catalyst system is an oligomeric compound which may be represented by the general formula (R3xe2x80x94Alxe2x80x94O), which is a cyclic compound, or may be R4(R5xe2x80x94Alxe2x80x94Oxe2x80x94)mxe2x80x94AlR62 which is a linear compound. An alumoxane is generally a mixture of both the linear and cyclic compounds. In the general alumoxane formula R3, R4, R5 and R6 are, independently a C1-C5 alkyl radical, for example, methyl, ethyl, propyl, butyl or pentyl and xe2x80x9cmxe2x80x9d is an integer from 1 to about 50. Most preferably, R3, R4, R5 and R6 are each methyl and xe2x80x9cmxe2x80x9d is at least 4. When an alkyl aluminum halide is employed in the preparation of the alumoxane, one or more R3-6 groups may be halide.
As is now well known, alumoxanes can be prepared by various procedures. For example, a trialkyl aluminum may be reacted with water, in the form of a moist inert organic solvent; or the trialkyl aluminum may be contacted with a hydrated salt, such as hydrated copper sulfate suspended in an inert organic solvent, to yield an alumoxane. Generally, however prepared, the reaction of a trialkyl aluminum with a limited amount of water yields a mixture of both linear and cyclic species of alumoxane.
Suitable alumoxanes which may be utilized in the catalyst systems of this invention are those prepared by the hydrolysis of a trialkylaluminum; such as trimethylaluminum, triethyaluminum, tripropylaluminum; triisobutylaluminum, dimethylaluminumchloride, diisobutylaluminumchloride, diethylaluminumchloride, and the like. The most preferred alumoxane for use is methylalumoxane (MAO). Methylalumoxanes having an average degree of oligomerization of from about 4 to about 25 (xe2x80x9cmxe2x80x9d=4 to 25), with a range of 13 to 25, are the most preferred.
The catalyst systems employed in the method of the invention comprise a complex formed upon admixture of the Group IV B transition metal component with an alumoxane component. The catalyst system may be prepared by addition of the requisite Group IV B transition metal and alumoxane components to an inert solvent in which olefin polymerization can be carried out by a solution, slurry or bulk phase polymerization procedure.
The catalyst system may be conveniently prepared by placing the selected Group IV B transition metal component and the selected alumoxane component, in any order of addition, in an alkane or aromatic hydrocarbon solventxe2x80x94preferably one which is also suitable for service as a polymerization diluent. Where the hydrocarbon solvent utilized is also suitable for use as a polymerization diluent, the catalyst system may be prepared in situ in the polymerization reactor. Alternatively, the catalyst system may be separately prepared, in concentrated form, and added to the polymerization diluent in a reactor. Or, if desired, the components of the catalyst system may be prepared as separate solutions and added to the polymerization diluent in a reactor, in appropriate ratios, as is suitable for a continuous liquid phase polymerization reaction procedure. Alkane and aromatic hydrocarbons suitable as solvents for formation of the catalyst system and also as a polymerization diluent are exemplified by, but are not necessarily limited to, straight and branched chain hydrocarbons such as isobutane, butane, pentane, hexane, heptane, octane and the like, cyclic and alicyclic hydrocarbons such as cyclohexane, cycloheptane, methylcyclohexane, methylcycloheptane and the like, and aromatic and alkyl-substituted aromatic compounds such as benzene, toluene, xylene and the like. Suitable solvents also include liquid olefins which may act as monomers or comonomers including ethylene, propylene, 1-butene, 1-hexene and the like.
In accordance with this invention optimum results are generally obtained wherein the Group IV B transition metal compound is present in the polymerization diluent in a concentration of from about 0.0001 to about 1.0 millimoles/liter of diluent and the alumoxane component is present in an amount to provide a molar aluminum to transition metal ratio of from about 1:1 to about 20,000:1. Sufficient solvent should be employed so as to provide adequate heat transfer away from the catalyst components during reaction and to permit good mixing.
The catalyst system ingredientsxe2x80x94that is, the Group IV B transition metal, the alumoxane, and polymerization diluentxe2x80x94can be added to the reaction vessel rapidly or slowly. The temperature maintained during the contact of the catalyst components can vary widely, such as, for example, from xe2x88x9210xc2x0 to 300xc2x0 C. Greater or lesser temperatures can also be employed. Preferably, during formation of the catalyst system, the reaction is maintained within a temperature of from about 25xc2x0 to 100xc2x0 C., most preferably about 25xc2x0 C.
At all times, the individual catalyst system components, as well as the catalyst system once formed, are protected from oxygen and moisture. Therefore, the reactions to prepare the catalyst system are performed in an oxygen and moisture free atmosphere and, where the catalyst system is recovered separately it is recovered in an oxygen and moisture free atmosphere. Preferably, therefore, the reactions are performed in the presence of an inert dry gas such as, for example, helium or nitrogen.
In a preferred embodiment of the process of this invention the catalyst system is utilized in the liquid phase (slurry, solution, suspension or bulk phase or combination thereof), high pressure fluid phase or gas phase polymerization of an olefin monomer. These processes may be employed singularly or in series. The liquid phase process comprises the steps of contacting an olefin monomer with the catalyst system in a suitable polymerization diluent and reacting said monomer in the presence of said catalyst system for a time and at a temperature sufficient to produce a polyolefin of high molecular weight.
The monomer for such process may comprise ethylene alone, for the production of a homopolyethylene, or ethylene in combination with an xcex1-olefin having 3 to 20 carbon atoms for the production of an ethylene-xcex1-olefin copolymer. Homopolymers of higher xcex1-olefin such as propylene, butene, styrene and copolymers thereof with ethylene and/or C4 or higher xcex1-olefins and diolefins can also be prepared. Conditions most preferred for the homo- or copolymerization of ethylene are those wherein ethylene is submitted to the reaction zone at pressures of from about 0.019 psia to about 50,000 psia and the reaction temperature is maintained at from about xe2x88x92100xc2x0 to about 300xc2x0 C. The aluminum to transition metal molar ratio is preferably from about 1:1 to 18,000 to 1. A more preferable range would be 1:1 to 2000:1. The reaction time is preferably from about 10 seconds to about 1 hour. Without limiting in any way the scope of the invention, one means for carrying out the process of the present invention for production of a copolymer is as follows: in a stirred-tank reactor liquid xcex1-olefin monomer is introduced, such as 1-butene. The catalyst system is introduced via nozzles in either the vapor or liquid phase. Feed ethylene gas is introduced either into the vapor phase of the reactor, or sparged into the liquid phase as is well known in the art. The reactor contains a liquid phase composed substantially of liquid xcex1-olefin comonomer, together with dissolved ethylene gas, and a vapor phase containing vapors of all monomers. The reactor temperature and pressure may be controlled via reflux of vaporizing xcex1-olefin monomer (autorefrigeration), as well as by cooling coils, jackets etc. The polymerization rate is controlled by the concentration of catalyst. The ethylene content of the polymer product is determined by the ratio of ethylene to xcex1-olefin comonomer in the reactor, which is controlled by manipulating the relative feed rates of these components to the reactor.
As before noted, a catalyst system wherein the Group IV B transition metal component is a titanium species has the ability to incorporate high contents of xcex1-olefin comonomers. Accordingly, the selection of the Group IV B transition metal component is another parameter which may be utlized as a control over the ethylene content of a copolymer within a reasonable ratio of ethylene to xcex1-olefin comonomer.